Multicarrier communication system, multicarrier communication apparatus and cqi reporting method

ABSTRACT

Provided is a multicarrier communication apparatus by which information quantity of CQI reporting can be reduced. In the apparatus, each CQI is recorded in a CQI table section ( 122 ) by being classified into a plurality of CQI groups by following a certain rule. A CQI selecting section ( 123 ) estimates fluctuation range and variance of reception qualities of the entire resource block to be reported, based on an SINR value outputted from a quality level calculating section ( 121 ). Then, based on the estimated values, the CQI selecting section selects a suitable CQI group in a first step, selects a suitable CQI value from among the CQIs included in the selected CQI group in a second step, and outputs the ID of the selected CQI group and the selected CQI value to a CQI generating section ( 124 ) . Based on such information, the CQI generating section ( 124 ) generates a CQI frame to be transmitted to a base station.

TECHNICAL FIELD

The present invention relates to a multicarrier communication system,multicarrier communication apparatus and CQI report method that adopt ascheme such as an OFDM (Orthogonal Frequency Division Multiplex) scheme.

BACKGROUND ART

To achieve a high system throughput in a communication system using anOFDM scheme, a method is under study whereby subcarriers are dividedinto a plurality of resource blocks (RB: which refers to a groupcomposed of a plurality of subcarriers and serve as an allocation unitduring scheduling) and users are allocated to the resource blocksaccording to a channel quality indicator (CQI) for each resource blockusing time-frequency scheduling.

In order to effectively obtain a multi-user diversity gain throughtime-frequency scheduling, one resource block is set smaller than acorrelation bandwidth. On the other hand, when the bandwidth of aresource block becomes small, the number of resource blocks increases.Effective frequency scheduling requires a CQI to be reported on a perresource block basis, and therefore when the number of resource blocksincreases, the amount of CQI report (amount of information) increasesand the overhead in uplink also becomes large. Furthermore, when thenumber of communication terminals increases, the proportion of CQI's inan uplink signal also increases. Moreover, M-ary modulation furtherincreases the number of selectable parameters, and therefore the amountof CQI report increases.

For example, Non-Patent Document 1 discloses a technique of reducing theamount of CQI information in uplink by limiting the number of resourceblocks (number of RBs) to be reported.

One such method selects N resource blocks in descending order ofreceived quality as resource blocks for which CQI's are to be reportedand reports CQI values corresponding to resource block identifiers(RB-ID) which specify those resource blocks. Furthermore, another methodputs together a plurality of resource blocks, sets an RB group for CQIreport and reports from each communication terminal only CQI's ofresource blocks included in the RB group. This limits the number ofresource blocks targeted for CQI report, and can thereby reduce theamount of CQI report.

When a transmission rate is relatively low and the number of resourceblocks to which data is allocated is small, this technique caneffectively reduce the amount of CQI report in uplink for communicationterminals to which resource blocks are allocated preferentially withoutsubstantially losing a multi-user diversity gain.

Non-Patent Document 1: “Physical Channels and Multiplexing in EvolvedUTRA Downlink” (R1-050590) , 3 GPP TSG-RAN WG1 contributory document,NTT DoCoMo, June 2005

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, the above-described technique requires CQI report on manyresource blocks for communication terminals having a relatively hightransmission rate and low allocation priority and communicationterminals to which resource blocks of good received quality are notalways allocated. That is, a communication terminal having a hightransmission rate also has a large number of allocated resource blocksand a communication terminal having low allocation priority is likely tobe allocated to an idle channel, and therefore the number of resourceblocks for which CQI's are reported must be increased. This results in aproblem that the effect of reducing the amount of CQI report islessened.

It is an object of the present invention to reduce the amount of CQIreport even when there are communication terminals having a relativelyhigh transmission rate and low allocation priority.

Means for Solving the Problem

The multicarrier communication system according to the present inventionthat causes a communicating party to report channel quality indicatorsaccording to received quality, adopts a configuration in which: thechannel quality indicators are divided beforehand into a plurality ofgroups according to information shown by the channel quality indicators;and a multicarrier communication apparatus selects a group from theplurality of groups according to the received quality, further selects achannel quality indicator from the group according to the receivedquality and reports group selection information showing the selectedgroup and channel quality indicator selection information showing theselected channel quality indicator.

Advantageous Effect of the Invention

According to the present invention, even when there are communicationterminals having a relatively high transmission rate and low allocationpriority, the amount of CQI report can be reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the main configuration of amulticarrier communication apparatus according to Embodiment 1;

FIG. 2 is a block diagram showing the main internal configuration of aCQI frame generating section according to Embodiment 1;

FIG. 3 shows an example of all CQI's available in the communicationsystem according to Embodiment 1;

FIG. 4 illustrates the data structure of a CQI table according toEmbodiment 1;

FIG. 5 shows the frame configuration of a transmission frame for CQIreport according to Embodiment 1;

FIG. 6A is a diagram illustrating a communication environment for whichthe CQI report method according to Embodiment 1 is suitable;

FIG. 6B is another diagram illustrating a communication environment forwhich the CQI report method according to Embodiment 1 is suitable;

FIG. 7 is a diagram illustrating the data structure of a CQI tableaccording to Embodiment 2;

FIG. 8 is another diagram illustrating the data structure of the CQItable according to Embodiment 2;

FIG. 9A is a diagram illustrating a communication environment for whichthe CQI report method according to Embodiment 2 is suitable;

FIG. 9B is another diagram illustrating a communication environment forwhich the CQI report method according to Embodiment 2 is suitable;

FIG. 10 illustrates the data structure of a CQI table according toEmbodiment 3;

FIG. 11A is a diagram illustrating a communication environment for whichthe CQI report method according to Embodiment 3 is suitable;

FIG. 11B is another diagram illustrating a communication environment forwhich the CQI report method according to Embodiment 3 is suitable;

FIG. 12 is a graph showing an existence probability of RB correspondingto a certain SINR;

FIG. 13A is a diagram illustrating resource blocks targeted for CQIreport according to Embodiment 4;

FIG. 13B is another diagram illustrating resource blocks targeted forCQI report according to Embodiment 4;

FIG. 14 is a block diagram showing the main internal configuration of aCQI frame generating section according to Embodiment 4;

FIG. 15 shows an example of a CQI table according to Embodiment 4;

FIG. 16 is a flowchart showing processing steps for a report CQIdetermining method according to Embodiment 4;

FIG. 17A is a diagram illustrating an amount of CQI report according toa CQI report method according to Embodiment 4;

FIG. 17B is another diagram illustrating an amount of CQI reportaccording to the CQI report method according to Embodiment 4; and

FIG. 17C is still another diagram illustrating an amount of CQI reportaccording to the CQI report method according to Embodiment 4.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail belowwith reference to the attached drawings. A case will be described withembodiments here as an example where an OFDM scheme is adopted asmulticarrier communication and a communication terminal whichcommunicates with a base station estimates received quality in downlinkand reports a CQI as channel quality information to the base station,but the present invention is not limited to this.

Embodiment 1

FIG. 1 is a block diagram showing the main configuration of amulticarrier communication apparatus (mobile station) according toEmbodiment 1 of the present invention.

The multicarrier communication apparatus according to this embodimenthas transmitting section 100, receiving section 110 and antenna 118.Furthermore, transmitting section 100 is provided with encoding section101, modulating section 102, radio transmission processing section 103.Receiving section 110 is provided with radio reception processingsection 111, GI removing section 112, FFT section 113, demodulatingsection 114, decoding section 115, channel response estimating section116 and CQI frame generating section 117.

The sections of the multicarrier communication apparatus according tothis embodiment operate as follows.

In receiving section 110, radio reception processing section 111receives a signal transmitted from a base station through antenna 118,converts the received signal to a baseband signal and outputs the signalto GI removing section 112. GI removing section 112 removes a guardinterval portion from the baseband received signal and outputs thisreceived signal to FFT section 113. FFT section 113 converts thereceived time domain signal into a frequency domain signal through afast Fourier transform (FFT) and outputs the result to demodulatingsection 114 and channel response estimating section 116. Demodulatingsection 114 performs demodulation processing according to apredetermined modulation scheme such as QPSK and 16QAM on the signal ofan information data sequence from which pilot signals and the like areremoved, out of the received signal subjected to fast Fourier transformprocessing, and outputs the demodulated signal to decoding section 115.Decoding section 115 performs error correcting processing according to apredetermined coding scheme such as turbo code on the signal from whichpilot signals and the like are removed, and extracts received data whichis the information data sequence, from the received signal.

Furthermore, channel response estimating section 116 receives a signal,such as a pilot signal, necessary for channel response estimation out ofthe received signal subjected to the fast Fourier transform processingand estimates a channel response on a per subcarrier basis. CQI framegenerating section 117 generates a CQI frame for CQI report to the basestation using the channel response estimation value estimated by channelresponse estimating section 116 and outputs the CQI frame totransmitting section 100. This CQI frame is used by the base station forfrequency scheduling, adaptive modulation and the like, and specifiesmodulation parameters (such as a modulation scheme, coding rate andtransmission power) of transmission data from the base station. Detailswill be described later.

On the other hand, in transmitting section 100, encoding section 101performs error correcting coding processing to uplink transmission dataand the CQI frame outputted from CQI frame generating section 117 andoutputs the encoded data to modulating section 102. Modulating section102 performs predetermined modulation Processing such as QPSK and 16QAMand secondary modulation processing (e.g., OFDM modulation) used inuplink and outputs the modulated signal to radio transmission processingsection 103. Radio transmission processing section 103 converts thebaseband transmission signal outputted from modulating section 102 to anRF (Radio Frequency) transmitting band signal and transmits this RFsignal through antenna 118.

FIG. 2 is a block diagram showing the main internal configuration ofabove-described CQI frame generating section 117.

Quality level calculating section 121 calculates an average SINR valuefor each resource block based on the frequency response of the channelon a per subcarrier basis estimated at channel response estimatingsection 116 and outputs the average SINR value to CQI selecting section123.

CQI table section 122 holds modulation parameters such as a modulationscheme, coding rate and transmission power as a CQI table in a ROM (ReadOnly Memory). In this CQI table, CQI's are divided into a plurality ofgroups (hereinafter “CQI group”) according to a certain rule and stored.In other words, this CQI table stores a plurality of CQI groups incombination with a plurality of CQI's included in the CQI groups. CQItable section 122 adaptively outputs content of the CQI table to CQIselecting section 123 according to the request from CQI selectingsection 123.

With reference to the above-described CQI table, CQI selecting section123 selects a CQI according to the received quality calculated atquality level calculating section 121 and outputs the CQI to CQIgenerating section 124. More specifically, CQI selecting section 123receives an average SINR value for each resource block from qualitylevel calculating section 121. CQI selecting section 123 estimates therange (fluctuation width) of received quality of all resource blockstargeted for report and a degree of variation (variance) in the receivedquality, from this SINR value for each resource block. CQI selectingsection 123 then selects a CQI in two stages based on these estimatedvalues. That is, CQI selecting section 123 selects an appropriate CQIgroup corresponding to the above-described estimated value as a firststage and then selects a CQI value corresponding to the above-describedestimated value from among CQI's included in the selected CQI group as asecond stage. Here, the CQI group is commonly applied to all resourceblocks, but a CQI further selected from within the selected groupcorresponds to each resource block. CQI selecting section 123 outputsidentification information (CQI group ID) showing the selected CQI groupand information related to the CQI selected from this group (a pluralityof CQI values corresponding to the respective resource blocks) to CQIgenerating section 124.

CQI generating section 124 generates a CQI frame to be transmitted tothe base station by combining CQI group ID and a CQI value for eachresource block outputted from CQI selecting section 123, and outputs theCQI frame to encoding section 101.

The CQI report method according to the above embodiment will bedescribed in detail using FIG. 3 and FIG. 4.

FIG. 3 shows an example of all CQI's available in the communicationsystem where the multicarrier communication apparatus according to thisembodiment is accommodated. Here, variations of modulation schemesinclude QPSK, 8PSK, 16QAM and 64QAM, and variations of coding rateinclude ⅓, ½, ⅔, ¾ and ⅚. Furthermore, the case is described here as anexample where communication is performed by duplicating (repeating)symbols to a plurality of symbols, and so a repetition factor (RF),which is the number of repetition symbols, is also defined, and it isassumed that RF=1, 2, and 4 is applied only in the case of a QPSK schemehere.

In the example of this figure, thirty types of CQI's or thirty one typesof CQI's including a CQI showing a state where communication is notpossible, are available as combinations. When the whole communicationsystem is observed, CQI variations in such a range exist, and so, whenCQI report is performed per resource block, the number of CQI bitsrequired for CQI report is five (=thirty-two combinations). Furthermore,when available transmission parameters such as transmission antennaswhen using antenna diversity and stream number when adopting a MIMO-SDM(Multi-Input/Multi-Output-Space Division Multiplexing) scheme, increase,available CQI's increase, and therefore the amount of CQI report furtherincreases.

Therefore, as already described, this embodiment selects a CQI whichbelongs to any one of CQI groups as a CQI to be actually used. That is,the actual CQI is selected from a CQI group which has feweralternatives, so that the amount of CQI report can be reduced.

To cover all kinds of channel environment of all communication terminalssupported by the communication system, CQI's are provided with a dynamicwide range of alternatives. However, when attention is focused on acertain communication terminal, the channel environment of thiscommunication terminal is limited, and necessary CQI's fall within amorelimited range. Especially, when instantaneous channel responses areconsidered, the necessary CQI's are more limited. Therefore, even whenthe range of alternatives of CQI's is limited as described above, theremay be few cases where throughput of the communication system decreases.

FIG. 4 illustrates the data structure of a CQI table according to thisembodiment. The method of setting a CQI group will also be described indetail using this figure.

Reference numeral 401 is a CQI table set such that CQI's available inthe communication system according to this embodiment (see FIG. 3) arearranged in descending order of required SINR', and, when CQI's have thesame transmission rate, one CQI having a lower required SINR isselected.

In this embodiment, CQI's of similar received quality are put togetheras one group. More specifically, based on CQI table 401, eight CQI's aregrouped into CQI groups 1 to 6. Reference numeral 402 shows CQI group 1set with CQI's having the highest required SINR's, and 403 shows CQIgroup 2 set with CQI's having the second highest required SINR's. CQIgroup 4 is set for CQI's having medium required SINR'S. Referencenumeral 404 shows CQI group 6 set with CQI's having the lowest requiredSINR's.

Furthermore, CQI's included in the CQI groups in this embodiment are setso as to overlap each other among groups. This makes it possible tosupport more diversified communication terminal channel environments.

Although a case has been described with this example where CQI's of thesame coding rate are put together as one group, a coding rate in onegroup may vary or the same modulation scheme may also be included in thesame group, if CQI's included in the groups cover a wide range ofreceived quality and intervals between required quality levels of CQI'sare set to be uniform to a certain degree.

FIG. 5 shows the frame configuration of a transmission frame for CQIreport according to this embodiment.

CQI frame generating section 117 generates a transmission frame for CQIreport as shown in this figure from a CQI group ID selected by CQIselecting section 123 and CQI bits corresponding to each resource block(information bits to identify each CQI).

Here, the number of bits X of the CQI group ID depends on the number ofCQI groups set in the system. That is, in the case of X bits, 2^(x)types of CQI groups can be set. Furthermore, the number of CQI bits Ycorresponding to each resource block depends on the number of CQI'sincluded in the CQI group. That is, in the case of Y bits, 2^(y) typesof CQI's can be set in one CQI group. For example, in the case of theCQI table shown in FIG. 4, by using this transmission frame for CQIreport, it is possible to reduce the number of required CQI bits tothree.

The amount of CQI report can be reduced further by reducing the numberof CQI groups or types (number) of CQI's included in each CQI group.

FIGS. 6A and 6B illustrate a communication environment for which the CQIreport method according to this embodiment is suitable.

The CQI groups according to this embodiment are grouped by CQI's havingsimilar received quality, and so these groups are suitable for acommunication terminal having channel performances with small receivedquality variations for each resource block as shown in FIGS. 6A and 6B,that is, a communication terminal having received quality performanceswith moderate frequency selective fading.

In this way, according to this embodiment, a plurality of CQI's aredivided into several CQI groups, and a CQI to be actually used isselected from these groups. CQI report is performed using two types ofinformation; identification information showing a selected group andidentification information showing a CQI selected in a group. Therefore,by reducing the number of CQI alternatives when deciding a CQI, it ispossible to reduce the number of bits necessary to identify a CQI andreduce the amount of CQI report. Reporting of group identificationinformation corresponds to reporting of CQI information with a lowdegree of accuracy as a first stage. Furthermore, reporting ofidentification information of a CQI selected in a group corresponds toreporting of CQI information with a high degree of accuracy as a secondstage. Here, CQI groups are commonly applied to all resource blocks, andCQI groups varying from one resource block to another are neverallocated. On the other hand, a CQI selected in each CQI group can takea value which varies from one resource block to another.

Furthermore, according to this embodiment, resource blocks targeted forCQI report are all resource blocks included in a communication band.That is, for all resource blocks, CQI's are reported within a selectedCQI group range. Therefore, the amount of CQI report can be reduced byreducing CQI alternatives while performing CQI report on all resourceblocks. That is, irrespective of the number of resource blocks to bereported, the amount of CQI report can be reduced at a fixed rate.

Furthermore, according to this embodiment, out of CQI's available in acommunication system, there is a range of CQI's available to amulticarrier communication apparatus such as a mobile station at acertain time point, and therefore CQI's which are currently not used orcannot be used are removed from the alternatives of CQI report, so thatthe number of CQI bits for each resource block can be reduced.

Furthermore, according to this embodiment, CQI's having similar receivedquality such as required SINR's are put together as one group.Therefore, it is possible to make finer and more accurate selections ofappropriate CQI's for communication terminals having little variation inreceived quality among resource blocks.

Furthermore, according to this embodiment, CQI's are divided into aplurality of CQI groups and stored beforehand in a CQI table based on acertain rule. These CQI groups are known between a transmittingapparatus and a receiving apparatus, that is, between a base station anda communication terminal. Therefore, it is not necessary to reportinformation as to how CQI's are specifically grouped.

Although a case has been described with this embodiment here as anexample where CQI groups are preset and fixed, CQI groups can also beadaptively set according to an environment where the communicationsystem is used, for example, outdoors or indoors in urban areas orsuburbs, or according to channel states of the connected communicationterminal. When the CQI groups are adaptively set, information of thesetting is periodically reported from the base station to thecommunication terminal and the like through broadcast channels and thelike.

Furthermore, although a case has been described with this embodiment asan example where CQI selecting section 123 selects a CQI according toreceived quality in two stages, that is, selects a CQI group at a firststage and selects an actual CQI from the group at a second stage, in thepresent invention, it is only necessary to form CQI information withtwo-stage information; identification information of a CQI group andidentification information of a CQI actually selected in this group, toreduce the amount of CQI report. Therefore, CQI selecting section 123may directly select a CQI according to received quality first, thenrecognize a CQI group where this selected CQI is included, and, based onthe reorganization, generate identification information of the CQI groupand identification information of the actually selected CQI.

Furthermore, although a case has been described with this embodiment asan example where a communication terminal selects a CQI group, it isalso possible to adopt a configuration where the base station specifiesa CQI group beforehand per communication terminal.

Embodiment 2

The configuration of a multicarrier communication apparatus according toEmbodiment 2 of the present invention has the same basic configurationas the multicarrier communication apparatus shown in Embodiment 1, andtherefore explanations thereof will be omitted, and only differencesfrom Embodiment 1, that is, the data structure of a CQI table will bedescribed below.

FIG. 7 and FIG. 8 illustrate the data structure of a CQI table accordingto this embodiment.

Reference numerals 701 and 801 show CQI tables showing CQI's availablein the communication system according to this embodiment. CQI's arearranged in descending order of required SINR's. Based on this CQI tablearranged in descending order of required SINR's, CQI groups 21 to 25 areset such that the number of CQI's included in each CQI group is eight.

More specifically, as shown by reference numeral 702, CQI group 21 iscomposed of CQI's showing all modulation schemes having coding rate R=⅚and a CQI showing that communication is not possible. Furthermore, asshown by reference numeral 703, CQI group 22 is composed of CQI'sshowing all modulation schemes having coding rate R=¾ and a CQI showingthat communication is not possible. Furthermore, as shown by referencenumeral 802, CQI group 25 is composed of CQI's showing all modulationschemes having coding rate R=⅓ and a CQI showing that communication isnot possible. The same applies to CQI groups 23 and 24.

By setting the CQI groups in this way, the range of required SINR's ofCQI's included in one CQI group can support a wide range from low SINR'sto high SINR's, and intervals between required SINR's among CQI's canalso be uniformly set. The number of CQI bits necessary for CQI reportis also three in this case as in the case of Embodiment 1.

In this way, according to this embodiment, a CQI group is composed ofCQI's with wide intervals between required received quality levels so asto cover a wide range of required received quality of CQI's in one CQIgroup. Therefore, it is possible to assign appropriate CQI'scorresponding to a wide range of required received quality forcommunication terminals having large variations in the received qualityamong resource blocks without being biased to partial required receivedquality and thereby improve the accuracy of CQI report.

FIGS. 9A and 9B illustrate a communication environment for which the CQIreport method according to this embodiment is suitable.

The CQI group according to this embodiment is suitable for communicationterminals as shown in FIGS. 9A and 9B having channel performances withlarge variations of the received quality among resource blocks, that is,communication terminals having received quality performances withsignificant frequency selective fading.

Embodiment 3

The configuration of a multicarrier communication apparatus according toEmbodiment 3 of the present invention also has the same basicconfiguration as the multicarrier communication apparatus shown inEmbodiment 1, and therefore explanations thereof will be omitted andonly differences from Embodiments 1 and 2, that is, the data structureof a CQI table will be described below.

FIG. 10 illustrates the data structure of a CQI table according to thisembodiment.

Reference numeral 1001 shows a diagram showing CQI's arranged indescending order of required SINR's available in the communicationsystem according to this embodiment. Based on this CQI table arranged indescending order of required SINR's, CQI groups where the number ofCQI's is limited to eight are set.

More specifically, as shown by reference numeral 1002, CQI group 31selects a plurality of CQI's with wide intervals between required SINR'sso as to include a plurality of CQI's having the highest required SINR's(indexes 30, 29, 28 and 25) and include several CQI's having lowrequired SINR's (indexes 23, 19, 14, and 9) in addition to the pluralityof CQI's having high required SINR's, and sets these CQI's in the samegroup.

Furthermore, as shown by reference numeral 1003, CQI group 32 performsthe setting so as to include CQI's having medium required SINR's(indexes 18, 15, 13, and 12) and include several CQI's having lowrequired SINR's (indexes 9, 7, and 4) as in the case of CQI group 31.

In this way, CQI groups 31 and 32 are composed of such CQI's that, whenthe required received quality becomes lower, the intervals betweenrequired received quality levels become wider. Especially in a range ofhigh required SINR's, such CQI's are selected that intervals of therequired SINR's between CQI's become narrower, and in a range of lowrequired SINR's, such CQI's are selected that intervals of requiredSINR's between CQI's become wider.

On the other hand, as shown by reference numeral 1004, CQI group 33 iscomposed of only CQI's having required SINR's equal to or lower than apredetermined level. This CQI group 33 has the same setting as group 6shown in Embodiment 1 (see FIG. 4).

In this way, this embodiment includes CQI's with equal intervals ingroups in a range of high required received quality, and includes CQI'scovering a wide range in groups in a range of low required receivedquality although intervals become wider. This allows the accuracy of CQIreport to be improved. For example, when it is assumed that CQI's ofindexes of 23, 19, 14 and 9 are not included in CQI group 31, ifactually required CQI's are outside the range of CQI group 31, that is,received quality for resource blocks is lower than the CQI of index 25,although these resource blocks are resource blocks where communicationis possible, “communication is not possible” is reported or appropriateCQI's cannot be reported, that is, CQI's of required received qualityhigher than the actual received quality are reported. As a result, it isnot possible to allocate transmission data or set appropriate modulationparameters for these resource blocks. However, adopting theabove-described configuration can cover a wide range of CQI's andthereby prevent this problem.

FIGS. 11A and 11B are diagrams illustrating a communication environmentfor which the CQI report method according to this embodiment issuitable.

FIG. 11A shows an example where received quality of a whole channel ishigh and influences of noise, interference power and the like are small,and therefore received quality range R31 where communication is possibleis wide. On the other hand, FIG. 11B shows an example where receivedquality of a whole channel is small and influences of noise,interference power and the like are large, and therefore receivedquality range R32 where communication is possible is narrow. The CQIgroups according to this embodiment are suitable for communicationterminals as shown in FIGS. 11A and 11B having such channel performancesthat an arrival wave becomes Rayleigh fading.

Furthermore, according to this embodiment, a CQI group is composed ofsuch CQI's that, when the required received quality becomes lower, theintervals of required received quality between CQI's gradually becomewider. This is for the following reason.

FIG. 12 is a graph showing an existence probability of resource blocksfor which CQI's showing required SINR's should be reported to a basestation. That is, this graph shows that, when the value of the existenceprobability decreases, the number of resource blocks for which CQI'sshowing those SINR's should be reported decreases. Here, this embodimentassumes a case where the channel is in a frequency selective Rayleighfading environment.

As shown in this figure, when a required SINR becomes lower, the numberof resource blocks (existence probability) for which corresponding CQI'sshould be reported decreases. Therefore, when the required SINR becomeslower, their CQI's are hardly used. Therefore, considering acontribution to effect, this embodiment makes a setting of lowering theaccuracy of CQI report (lowering resolution of reported CQI) so as towiden intervals of required SINR's between CQI's in an area of lowrequired SINR's. This allows the range of required received qualitycovered by CQI's to be widened while maintaining an expected value ofthe accuracy of CQI report.

Furthermore, according to this embodiment, when CQI groups are comparedwith each other, required received quality corresponding to the CQI's isnot distributed in the same way. However, even in such a case, thenumber of CQI bits necessary for CQI report is three.

Although a case has been described with this embodiment as an examplewhere, when the required received quality becomes lower, the intervalsof received quality between CQI's gradually become wider, a setting mayalso be made such that the intervals of the received quality becomewide, although the intervals of the received quality are equal, in arange where the required received quality is low. This is because such aconfiguration also allows the object of covering a wide range ofrequired received quality to be attained.

Embodiment 4

FIGS. 13Aand 13B illustrate resource blocks targeted for CQI reportaccording to Embodiment 4 of the present invention. FIGS. 13A and 13Bshow received quality performances (channel responses) of the resourceblocks and also show resource blocks targeted for report by diagonalline.

FIG. 13A shows an example where each communication terminal selects apredetermined number “four” of resource blocks in descending order ofreceived quality and performs CQI report on these resource blocks. Inthis example, fluctuation width R41 of CQI's among resource blockstargeted for report is small.

FIG. 13B shows an example where each communication terminal selects anappropriate RB group with the highest transmission efficiency from RBgroups #1 to #4 and performs CQI report on this RB group. Thecommunication terminal selects RB group #2, and so fluctuation width R42of CQI's among resource blocks targeted for report becomes small.

In this way, in this embodiment, the number of resource blocks targetedfor report varies depending on various conditions. A plurality of CQItables are also provided according to the number of resource blocks, andthese are used differently depending on the number of resource blocks.

The configuration of a multicarrier communication apparatus according tothis embodiment has the same basic configuration as the multicarriercommunication apparatus shown in Embodiment 1, and thereforeexplanations thereof will be omitted and CQI frame generating section117 a which has the configuration different from Embodiment 1 will bedescribed below.

FIG. 14 is a block diagram showing the main internal configuration ofCQI frame generating section 117 a. The same components as in CQI framegenerating section 117 shown in Embodiment 1 are assigned the samereference numerals and explanations thereof will be omitted, andcomponents having similar functions are shown by assigning alphabets inaddition to the same reference numerals.

This CQI frame generating section 117 a receives report RB numberinformation determined from a report RB number determining section (notshown).

CQI table section 122 a holds a plurality of CQI tables corresponding tothe number of resource blocks to be reported. Details will be describedlater.

CQI selecting section 123 a selects an appropriate CQI table from amongCQI tables held in CQI table section 122 a based on the number of reportRBs to be inputted and determines a CQI value for each resource blocktargeted for report using the CQI table.

FIG. 15 shows an example of the CQI table held in CQI table section 122a. Furthermore, CQI table section 122 a also holds other types of CQItables, and the CQI table shown in FIG. 4 is one such example.

In these tables, although each CQI group is composed of CQI's havingsimilar required received quality, the CQI table shown in FIG. 15 setsthe number of CQI's included in each CQI group to four unlike the CQItable shown in FIG. 4.

When the number of resource blocks targeted for report becomes smaller,the variation of received quality in these resource blocks becomessmaller, and so the CQI table shown in FIG. 15 limits the number ofCQI's included in each CQI group according to the reduction in thenumber of resource blocks. In the example of FIG. 15, the number ofnecessary CQI bits is two.

FIG. 16 is a flowchart showing processing steps of a report CQIdetermining method according to this embodiment.

This embodiment compares the number of report RBs with a predeterminedthreshold (ST4010), and, when the number of report RBs is greater thanthe predetermined threshold, determines an appropriate CQI table fromamong ordinary CQI tables (ST4020). Here, the “ordinary CQI table”refers to a CQI table which does not support a reduction in the numberof resource blocks, and, for example, the CQI tables shown inEmbodiments 1 to 3 correspond to this CQI table.

On the other hand, in ST4010, when the number of report RBs is equal toor smaller than the predetermined threshold, an appropriate CQI table isdetermined from among a plurality of CQI tables (an example is shown inFIG. 14) set in accordance with a reduction in the number of resourceblocks (ST4030).

Next, using the determined CQI table, an appropriate CQI group isselected according to the required received quality (ST4040), and anappropriate CQI for each resource block to be reported is determinedfrom the selected CQI group (ST4050).

FIGS. 17A, 17B and 17C are diagrams illustrating the amount of CQIreport of the CQI report method according to this embodiment.

As shown in the above-described flow, the CQI table to be used variesdepending on whether the number of resource blocks targeted for reportis greater or smaller than a predetermined threshold. Therefore, thenumber of bits showing CQI group ID and the number of CQI bits for eachresource block also vary depending on the difference in the CQI table.

When the number of resource blocks targeted for report is greater thanthe predetermined threshold, the transmission frame is as shown in FIG.17A, for example. The figure shows an example where the number of CQIgroups is sixteen types and the number of CQI's included in each CQIgroup is eight. Therefore, CQI group ID is expressed with four bits andCQI information corresponding to each resource block is expressed withthree bits.

On the other hand, when the number of resource blocks targeted forreport is equal to or smaller than the predetermined threshold, thetransmission frames are as shown in FIG. 17B or FIG. 17C, for example.FIG. 17B shows a case where a predetermined number of resource blocksare selected in descending order of received quality, and FIG. 17C showsa case where an RB group of the highest received quality is selected.The figure here shows an example where the number of CQI groups is eighttypes, and the number of CQI's included in each CQI group is four (whenthe CQI table shown in FIG. 15 is used). Therefore, CQI group ID isexpressed with three bits, and CQI information corresponding to eachresource block is expressed with two bits.

In this way, according to this embodiment, when the number of resourceblocks targeted for CQI report decreases, the number of CQI's includedin each CQI group also decreases accordingly. By this means, it ispossible to reduce the amount of CQI report while preventing theaccuracy of CQI report from decreasing.

The embodiments of the present invention have been described.

The multicarrier communication system, multicarrier communicationapparatus and CQI report method according to the present invention arenot limited to the above-described embodiments, and variousmodifications thereof are possible. For example, the embodiments havedisclosed a plurality of CQI tables suitable for a variety of channelstates, that is, a plurality of types of CQI grouping method accordingto the channel environment. Therefore, the present invention can berealized by combining these methods as appropriate.

More specifically, it is possible to set both a CQI group composed of aset of CQI' shaving similar received quality and a CQI group composed ofa set of CQI's with wide intervals between received quality levels, outof CQI selection candidates, select a CQI group common to resourceblocks suitable for received quality of all resource blocks targeted forreport from a mobile station and perform CQI report. By this means, themobile station can use an appropriate CQI group suitable for receivedquality for CQI report while reducing the number of CQI bits. That is,it is possible to effectively reduce the amount of CQI report withoutlosing substantially any multi-user diversity gain.

For example, as shown in FIG. 6A, when a variation of received qualityamong resource blocks is small and the received quality is high, a CQIgroup composed of CQI's having similar required SINR's and CQI's havinghigh required SINR's is selected. On the other hand, as shown in FIG.11A, when a variation of received quality among resource blocks islarge, a group which allows more appropriate CQI report on the resourceblocks is selected out of CQI groups composed of CQI's having largeintervals between required SINR'. Here, “more appropriate” means, forexample, making a setting so as to minimize the difference between thereceived quality of each resource block and a required SINR or setting aCQI group that maximizes the transmission efficiency.

The multicarrier communication apparatus according to the presentinvention can be provided to a communication terminal apparatus and abase station apparatus in a mobile communication system, and can therebyprovide a communication terminal apparatus, base station apparatus andmobile communication system having operations and effects similar tothose described above.

Furthermore, the multicarrier communication system, multicarriercommunication apparatus and CQI report method according to the presentinvention can also be used in communication systems adoptingmulticarrier schemes other than OFDM.

The number of CQI groups and the number of CQI bits included in a CQIgroup are not limited to the values shown in the embodiments.

Also, although cases have been described with the above embodiment asexamples where the present invention is configured by hardware. However,the present invention can also be realized by software. For example, itis possible to implement the same functions as in the multicarriercommunication apparatus of the present invention by describingalgorithms of the CQI report methods according to the present inventionusing the programming language, and executing this program with aninformation processing section by storing in memory.

Each function block employed in the description of each of theaforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip.

“LSI” is adopted here but this may also be referred to as “IC”, “systemLSI”, “super LSI”, or “ultra LSI” depending on differing extents ofintegration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand settings of circuit cells within an LSI can be reconfigured is alsopossible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The present application is based on Japanese Patent Application No.2005-238952, filed on Aug. 19, 2005, the entire content of which isexpressly incorporated by reference herein.

INDUSTRIAL APPLICABILITY

The multicarrier communication system, multicarrier communicationapparatus and CQI report method according to the present invention aresuitable for use in a communication terminal apparatus, base stationapparatus and the like in a mobile communication system.

1. A multicarrier communication system that causes a communicating partyto report channel quality indicators according to received quality,wherein: the channel quality indicators are divided beforehand into aplurality of groups according to information shown by the channelquality indicators; and a multicarrier communication apparatus selects agroup from the plurality of groups according to the received quality,further selects a channel quality indicator from the group according tothe received quality and reports group selection information showing theselected group and channel quality indicator selection informationshowing the selected channel quality indicator.
 2. A multicarriercommunication apparatus that reports channel quality indicatorsaccording to received quality, the apparatus comprising: a channelquality indicator table that stores the channel quality indicatorsdivided into a plurality of groups according to information shown by thechannel quality indicators; a group selecting section that selects agroup from the plurality of groups according to the received quality; achannel quality indicator selecting section that selects a channelquality indicator from the selected group according to the receivedquality; and a transmitting section that transmits group selectioninformation showing the selected group and channel quality indicatorselection information showing the selected channel quality indicator. 3.The multicarrier communication apparatus according to claim 2, whereinthe channel quality indicator table stores the channel qualityindicators having required received quality included in a predeterminedrange, as a same group.
 4. The multicarrier communication apparatusaccording to claim 2, wherein the channel quality indicator table storesthe channel quality indicators such that required received quality isdistributed in the groups.
 5. The multicarrier communication apparatusaccording to claim 2, wherein the channel quality indicator tablestores, as a same group, the channel quality indicators such that, whenthe required received quality becomes lower, intervals between therequired received quality levels become wider.
 6. The multicarriercommunication apparatus according to claim 2, wherein the channelquality indicator table stores groups including all channel qualityindicators when required received quality is equal to or higher than apredetermined level, and stores groups including channel qualityindicators such that the required received quality is distributed whenthe required received quality is less than the predetermined level.
 7. Achannel quality indicator table used in a multicarrier communicationapparatus that reports or receives channel quality indicators accordingto received quality, wherein: the channel quality indicators are dividedinto a plurality of groups according to information shown by the channelquality indicators and stored; and information mutually identifying theplurality of groups is used for channel quality indicator report.
 8. Acommunication terminal apparatus comprising the multicarriercommunication apparatus according to claim
 2. 9. A base stationapparatus comprising the multicarrier communication apparatus accordingto claim
 2. 10. A channel quality indicator report method for reportingchannel quality indicators according to received quality, the methodcomprising: selecting a group according to the received quality fromgroups obtained by dividing the channel quality indicators into aplurality of groups according to information shown by the channelquality indicators; selecting a channel quality indicator from theselected group according to the received quality; and transmitting groupselection information showing the selected group and channel qualityindicator selection information showing the selected channel qualityindicator.